The present invention relates to an improved method for forming soft magnetic underlayers for magnetic recording media having uniaxial anisotropy and to improved magnetic recording media including such uniaxially anisotropic soft magnetic underlayers. The present invention is of particular utility in the manufacture of high areal recording density perpendicular magnetic recording media, e.g., hard disks, which exhibit substantially reduced Barkhausen noise.
Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the recording density, i.e., bit density of the magnetic media. In this regard, so-called xe2x80x9cperpendicularxe2x80x9d recording media have been found to be superior to the more conventional xe2x80x9clongitudinalxe2x80x9d media in achieving very high bit densities. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically a layer of a magnetic material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a xe2x80x9csingle-polexe2x80x9d magnetic transducer or xe2x80x9cheadxe2x80x9d with such perpendicular magnetic media.
It is well-known that efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a relatively thick (i.e., as compared to the magnetic recording layer), magnetically xe2x80x9csoftxe2x80x9d underlayer, i.e., a magnetic layer having relatively low coercivity, such as of a NiFe alloy (Permalloy), between the non-magnetic substrate, e.g., of glass, aluminum (Al) or an Al-based alloy, and the xe2x80x9chardxe2x80x9d magnetic recording layer, e.g., of a cobalt-based alloy (e.g., a Coxe2x80x94Cr alloy) having perpendicular anisotropy. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the hard, perpendicular magnetic recording layer. In addition, the magnetically soft underlayer reduces susceptibility of the medium to thermally-activated magnetization reversal by reducing the demagnetizing fields which lower the energy barrier that maintains the current state of magnetization.
A typical perpendicular recording system 10 utilizing a vertically oriented magnetic medium 1 with a relatively thick soft magnetic underlayer, a relatively thin hard magnetic recording layer, and a single-pole head is illustrated in FIG. 1, wherein reference numerals 2, 3, 4, and 5, respectively, indicate the substrate, soft magnetic underlayer, at least one non-magnetic interlayer, and vertically oriented, hard magnetic recording layer of perpendicular magnetic medium 1, and reference numerals 7 and 8, respectively, indicate the single and auxiliary poles of single-pole magnetic transducer head 6. Relatively thin interlayer 4 (also referred to as an xe2x80x9cintermediatexe2x80x9d layer), comprised of one or more layers of non-magnetic materials, serves to (1) prevent magnetic interaction between the soft underlayer 3 and the hard recording layer 4 and (2) promote desired microstructural and magnetic properties of the hard recording layer. As shown by the arrows in the figure indicating the path of the magnetic flux xcfx86, flux xcfx86 is seen as emanating from single pole 7 of single-pole magnetic transducer head 6, entering and passing through vertically oriented, hard magnetic recording layer 5 in the region above single pole 7, entering and travelling along soft magnetic underlayer 3 for a distance, and then exiting therefrom and passing through vertically oriented, hard magnetic recording layer 5 in the region above auxiliary pole 8 of single-pole magnetic transducer head 6. The direction of movement of perpendicular magnetic medium 1 past transducer head 6 is indicated in the figure by the arrow above medium 1.
With continued reference to FIG. 1, vertical lines 9 indicate grain boundaries of each polycrystalline (i.e., granular) layer of the layer stack constituting medium 1. As apparent from the figure, the width of the grains (as measured in a horizontal direction) of each of the polycrystalline layers constituting the layer stack of the medium is substantially the same, i.e., each overlying layer replicates the grain width of the underlying layer. Not shown in the figure, for illustrative simplicity, are a protective overcoat layer, such as of a diamond-like carbon (DLC) formed over hard magnetic layer 5, and a lubricant topcoat layer, such as of a perfluoropolyethylene material, formed over the protective overcoat layer. Substrate 2 is typically disk-shaped and comprised of a non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as Alxe2x80x94Mg having an NiP plating layer on the deposition surface thereof, or substrate 2 is comprised of a suitable glass, ceramic, glass-ceramic, polymeric material, or a composite or laminate of these materials; underlayer 3 is typically comprised of an about 2,000 to about 4,000 xc3x85 thick layer of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, etc.; and hard magnetic layer 5 is typically comprised of an about 100 to about 250 xc3x85 thick layer of a Co-based alloy including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, and B, iron oxides, such as Fe3O4 and xcex4-Fe2O3, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 xc3x85 thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, and Pt, and each of the alternating thin, non-magnetic layers of Pd or Pt is about 1 xc3x85 thick. Each type of hard magnetic recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1st type) and interfacial anisotropy (2nd type).
A significant problem and drawback associated with the utilization of soft magnetic underlayers, such as layer 3 shown in FIG. 1, is the generation of noise resulting from, inter alia, pinning and unpinning (i.e., motion) of the magnetic domain walls thereof, termed xe2x80x9cBarkhausen noisexe2x80x9d, which noise adversely affects performance characteristics of magnetic media, particularly high bit density magnetic media.
Accordingly, there exists a need for an improved method for manufacturing high bit density perpendicular magnetic information/data recording, storage, and retrieval media including magnetically soft underlayers, but which exhibit no, or at least substantially reduced, Barkhausen noise. In addition, there exists a need for improved, high bit density perpendicular magnetic recording media employing magnetically soft underlayers which exhibit no, or at least substantially reduced, Barkhausen noise, which media can be readily and economically fabricated by means of conventional manufacturing techniques and instrumentalities.
The present invention addresses and solves problems attendant upon the use of magnetically soft underlayers in the manufacture of high bit density perpendicular magnetic media, e.g., generation of Barkhausen noise, while maintaining all structural and mechanical aspects of high bit density recording technology. Moreover, the magnetic media of the present invention can be fabricated by means of conventional manufacturing techniques, e.g., sputtering.
An advantage of the present invention is an improved method of manufacturing a magnetic recording medium having no, or at least substantially reduced, Barkhausen noise.
Another advantage of the present invention is an improved method of manufacturing a high areal density, perpendicular magnetic recording medium wherein Barkhausen noise is at least substantially suppressed.
Still another advantage of the present invention is an improved magnetic recording medium with no, or at least substantially reduced, Barkhausen noise.
Yet another advantage of the present invention is an improved high areal density, perpendicular magnetic recording medium wherein Barkhausen noise is at least substantially suppressed.
A still further advantage of the present invention is an improved disk drive comprising an improved high areal density, perpendicular magnetic recording medium having suppressed Barkhausen noise.
Additional advantages, aspects, and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a method of manufacturing a magnetic recording medium having no, or at least substantially reduced, Barkhausen noise, comprising the sequential steps of:
(a) providing a non-magnetic substrate having a surface;
(b) providing the surface of the substrate with a unidirectional texture pattern;
(c) forming an underlayer of a soft magnetic material over the unidirectional texture pattern, the layer of soft magnetic material having positive magnetostriction and uniaxial magnetic anisotropy and including a multiplicity of magnetic domains; and
(d) forming a magnetic recording layer of a hard magnetic material over the underlayer;
wherein the uniaxial magnetic anisotropy of the underlayer of soft magnetic material is sufficiently large to orient the magnetic domains thereof along the axis of uniaxial magnetic anisotropy and thereby restrict domain wall formation and/or movement, whereby generation of Barkhausen noise in the soft underlayer is suppressed.
According to embodiments of the present invention, step (a) comprises providing a disk-shaped substrate having a pair of opposed surfaces; step (b) comprises providing at least one of the pair of surfaces of the disk-shaped substrate with a circumferentially extending texture pattern; step (c) comprises forming an underlayer of a soft magnetic material having radial uniaxial magnetic anisotropy over the texture pattern; and step (d) comprises forming a layer of a hard magnetic material having perpendicular magnetic anisotropy.
In accordance with particular embodiments of the present invention, step (a) comprises providing a disk-shaped substrate comprising a non-magnetic material selected from the group consisting of Al, Al-based alloys, NiP-plated Al, other non-magnetic metals, other non-magnetic alloys, glass, ceramics, polymers, glass-ceramics, and composites and/or laminates thereof, step (b) comprises mechanically texturing the at least one surface of the substrate, e.g., step (b) comprises mechanically texturing the at least one surface of the substrate utilizing a slurry of abrasive particles dispensed on an absorbent and compliant polishing pad or tape, to form a circumferentially oriented texture pattern comprising a plurality of concentric, circularly-shaped grooves extending to a depth below the substrate surface, adjacent grooves of the pattern being spaced apart a preselected distance; step (c) comprises forming an underlayer of a soft magnetic material selected from the group consisting of Ni, NiFe, Co, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, etc., e.g., step (c) comprises forming an underlayer comprising a NiFe alloy having a Fe content from about 20 to about 60 wt. % and (111) texture, as by DC magnetron sputtering of a NiFe target having a Fe content from about 20 to about 60 wt. %; step (d) comprises forming a layer of hard magnetic material comprising Co alloyed with one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, and B, an iron oxide, such as Fe3O4 and xcex4-Fe2O3, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 xc3x85 thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, and Pt, and each of the alternating thin, non-magnetic layers of Pd or Pt is about 1 xc3x85 thick.
According to further embodiments of the present invention, step (a) comprises providing a substrate comprised of NiP-plated Al; step (b) comprises mechanically texturing the at least one surface of the substrate utilizing a slurry containing abrasive particles having a size of from about 800 to about 2,500 xc3x85 to form a circumferentially oriented texture pattern comprising a plurality of concentric, circularly-shaped grooves extending below the substrate surface to a depth from about 50 to about 150 xc3x85, adjacent grooves of the pattern being spaced apart 2,000 xc3x85; step (c) comprises DC magnetron sputter depositing a magnetically soft underlayer of a NiFe alloy having a Fe content of from about 20 to about 60 wt. %, a thickness from about 2,000 to about 4,000 xc3x85, (111) texture, and radial uniaxial magnetic anisotropy; and step (d) comprises forming a layer of a Co-based hard magnetic material having a thickness from about 100 to about 250 xc3x85.
According to another aspect of the present invention, a magnetic recording medium wherein Barkhausen noise is at least substantially suppressed, comprises:
(a) a non-magnetic substrate having a surface including a unidirectional texture pattern;
(b) an underlayer of a soft magnetic material formed over the unidirectionally textured surface, the layer of soft magnetic material having positive magnetostriction and unniaxial magnetic anisotropy and including a plurality of magnetic domains; and
(c) a magnetic recording layer of a hard magnetic material formed over the underlayer of soft magnetic material;
wherein the uniaxial magnetic anisotropy of the underlayer of soft magnetic material is sufficiently large to orient the magnetic domains thereof along the axis of uniaxial anisotropy and thereby restrict domain wall formation and/or movement, whereby generation of Barkhausen noise in the soft underlayer is suppressed.
According to embodiments of the present invention, substrate (a) is a disk-shaped substrate having a pair of opposed surfaces, and the unidirectional texture pattern is a mechanically formed, circumferentially oriented pattern comprising a plurality of concentric, circularly-shaped grooves; underlayer (b) of soft magnetic material is radially magnetically anisotropic; and magnetic recording layer (c) of hard magnetic material is perpendicularly magnetically anisotropic.
In accordance with particular embodiments of the present invention, substrate (a) comprises a non-magnetic material selected from the group consisting of Al, Al-based alloys, NiP-plated Al, other non-magnetic metals, other non-magnetic alloys, glass, ceramics, polymers, glass-ceramics, and composites and/or laminates thereof, and the circumferentially oriented texture pattern comprises a plurality of concentric, circularly-shaped grooves extending below the substrate surface to a depth from about 50 to about 150 xc3x85, with adjacent grooves of the pattern being spaced apart about 2,000 xc3x85; underlayer (b) of soft magnetic material comprises a material selected from the group consisting of Ni, NiFe, Co, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, and FeSiAlN, and magnetic recording layer (c) of hard magnetic material comprises Co alloyed with one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, and B, an iron oxide, such as Fe3O4 and xcex4-Fe2O3, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 xc3x85 thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, and Pt, and each of the alternating thin, non-magnetic layers of Pd or Pt is about 1 xc3x85 thick.
According to further embodiments of the present invention, substrate (a) comprises NiP-plated Al; underlayer (b) of soft magnetic material comprises a NiFe alloy having a Fe content of from about 20 to about 60 wt. %, a thickness from about 2,000 to about 4,000 xc3x85 and (111) texture; magnetic recording layer (c) of hard magnetic material has a thickness from about 100 to about 250 xc3x85; and the magnetic recording medium further comprises: (d) a protective overcoat layer on the magnetic recording layer (c); and (e) a lubricant topcoat over the protective overcoat.
According to a further aspect of the present invention, a disk drive comprises the above-described disk-shaped perpendicular magnetic recording medium, wherein the easy axis of magnetization of the underlayer (b) of soft magnetic material is aligned in the radial direction of the disk-shaped substrate.
According to still another aspect of the present invention, a magnetic recording medium comprises:
(a) a non-magnetic substrate including a surface with a soft underlayer formed thereover; and
(b) means for suppressing Barkhausen noise in the soft underlayer.
According to embodiments of the present invention, the magnetic recording medium further comprises a layer of a hard magnetic material having perpendicular anisotropy; the substrate is disk-shaped; and the surface of the substrate includes a circumferentially oriented texture pattern.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not limitative.